Palladium complexes as photographic emulsion stabilizers



Patented June 7, 1949 TENT OFFICE PALLADIUM COMPLEXES AS PHOTO- GRAPHIC,EMULSION STABILIZERS Robert E. Stauifer and William F. Smith, Rochester,N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., acorporation of New Jersey No Drawing. Application March 5, 1948, SerialNo. 13,352

This invention relates to fog-inhibiting agents and stabilizers forphotographic emulsions and to photographic emulsion-s containing them.

It is known that photographic emulsions, particularly ultra-sensitiveemulsions or those containing optical sensitizers exhibit a tendency toform upon development a deposit of silver in the emulsion. This depositextends more or less uniformly over the entire emulsion and is known asfog. Photographic fog is of two types: local and general. Local fog isformed by exposure of the film or plate at undesired points as by alight leak in the camera. General fog is formed in a number of ways. Itmay be caused by. the

conditions under which the film or plate is stored,

such as conditions of high temperature or humidity or unusually longtime of storage. The nature of the emulsion may also produce general fogas well as the conditions of development of the emulsion as bydevelopment for protracted periods of time or at temperatures abovenormal. We are primarily concerned with fog and sensitivity changesproduced in films or plates on development after storage under adverseconlcjitirons of high temperature and humidity or General fog and lossof sensitivity of the emulsion are especially likely to occur when thesensitive material is stored under conditions other than ideal, that is,under conditions of high temperature and humidity as in tropicalregions.

It is an object of the invention to provide novel anti-fogging orfog-inhibiting compounds for emulsions. A further object is to provideantifogging agents which stabilize the initial sensitivity of theemulsion. A still further object is to provide anti-fogging agents whichimprove the keeping of the emulsion in tropical regions. Other objectswill appear from the following description of our invention.

' These objects are accomplished by incorporating in a silver halideemulsion an anionic palladium complex salt such as alkali metal oralkaline earth metal thiocyanato palladites, nitritopalladites,bromo-nitritopalladates, and ammonlum nitritopalladite. For example, wemay use potassium thiocyanato palladite, mPd(CNS)4; calcium thiocyanatopalladite, CaPd(CNS)4; potassium nitrito palladite, K2Pd(NO2)4; bariumnitrito palladite, BaPd(NO2)4; potassium bromonitrito palladate,K2PdBr2(NO2)4, or ammonium nitritopalladite, (NH4)2Pd(NO2)4. Othersimilar anionic palladium complexes which have not been satisfactory,particularly because of fog- 5 Claims. "(01. 95-7) -2 ging properties ordesensitizing action on the photographic emulsion include ammonium andpotassium cyano palladites and ammonium thiocyanato palladite.

The object of our invention is to maintain the sensitivity and fog ofsilver halide emulsion at or close to initial optimum values underkeeping conditions of high temperature and humidity. The fog inhibitorswhich we propose to use are added to the emulsion during the process ofmanufacture to avoid loss of sensitivity and to inhibit the growth ofincubation or keeping fog with passage of time under non-idealconditions of storage.

A solution of the compounds of the invention when added in suitableconcentration before coating to unsensitized or optically sensitizedphotographic emulsions does notaiiect appreciably the sensitometricvalues for sensitivity and fog when measurements are made soon aftercoating. When sensitometric measurements are made after appreciableintervals of time under tropical or dry conditions of storage atelevated temperatures, however, the compounds stabilize photographicspeed and in certain cases maintain fog at a low level.

-The preparation of silver halide emulsions involves three separateoperations, (1) the emulsification and digestion or ripening of thesilver halide, (2) the freeing of the emulsion from excess soluble saltsusually by washing, (3) the second digestion or after-ripening to obtainincreased sensitivity (Mees, The Theory of the Photographic Process,1942). We prefer to add the fog-inhibiting agents after the finaldigestion or after-ripening although they may be added before digestion.The most useful concentration range of fog inhibitor is from 0.26 to 3.9gm. of fog inhibitor per kilogram of silver nitrate used in making theemulsion and converted to silver halide. This amount will vary, e. g.,depending upon the particular silver halide used.

'- The antifoggant and stabilizing action was determined by incubationof the emulsions under simulated tropical conditions and also byincubation in dry heat at F. for various lengths of time from 6 days to2 months. The results of these ageing tests are tabulated below and arecompared with the initial speed, gamma and fog of the emulsion withoutth stabilizing compounds. The tests from which the following tabulationwas made used a high-speed orthochromatic negative type of emulsionexposed on an EastmanfI ype sensitometer' and develq oped for fiveminutes in a developer of the following composition:

Water to one liter.

The results of the comparative tsfi -are as It will be noted from thedata in the above table that the improvement in fog and speed stabilityusing the compounds of the invention is appreciable as compared withemulsions containl-ii'g'ho inhibitor. Anothefadv'antage'of our inventionis that the compounds may be prepared easily and with high puritycompared to organic types of inhibitors. Another and perhaps chiefadvantage -'is 'the"greater extent of stabilizing whomever-'11: widerange of climatic conditions.

In use, the fog inhibitor is dissolved in water follows:

Original Y Gdays 12min Gms. of compound er Kg.AgNs (con- 1G2 verted toAg )inemulston H 10/1 G F Gamma Fog Speem I ammo. og

None -,1,15o; 1.11, .12, 590 1.42 .16 K1Pd(CNS)4, 1.250... 91D; 11 1.29.12 175 1.42 .16 KzPd(NO7)4 1.250. 795 1.35 .16 650 1.43 .24 KzPdBmNm, 1910 1. 21 .14 710 1. 39 19 Nodal-"0145.- Slbff i.3(5)? 1 1 1 N .PdN.411? .4-..1, EN i 1,500- 1 1.15 .13= 725- 1.35 .15

1 Control test sample for samples 6 and 7.

Examples of the method oi preparatiomand use of the compoundsorthemvehuta are-elven 40 The compound was added to the emulSiondn'the-"quantity shown in the tabla above and the emiilsion containing the usual'hardener and 1 sensitizew was coa'ted on a glass*plate driei exposedand developed. Other' 'sam'ples of the 'eniuIsi'On were aged andprocessed with =the results shown in the above 'table. M

Ebz'ampl' 2 Potassium nitrito 'paniaditew'as" prepared one yellowcrystals bji reacting 'a'" solut on" or emulsion and tested "with" theresults snow-11' i1? 0 the table above."

Ezdviifil '3 Ammonium nitritopal-lad-ite was--prepared gbyreactingammonium hexachloropalladateywith-asolution of potassiumnitriteand'aminonium chlo ride and after incorporation-Auto anemulsionwas tested with the results showfi' inthe "tatile'."

Example-'4 Potassium bromo-nitiitopanaaate was prepared" 1 n'riepr nafecmina-iw 1 ata colnvenient concentration and added to-a meltedel'atino-silver halide photographic emul-"- sion-in quantitiesranging-up =to about 3. gms/ perkilogra rrrof silver nitrate convertedto silver" halide. The emulsion is coated ona suitable supv 1 por-t,glass;-fi1m,- or -other,- and dried inanormal fashion; 7 I

We'also contemplate as a part of our invention those cases where itsdesirable-to coat theantifog'gant in a colloid layer such as'gelatin oneither or both sides of or also in the silver halide emul si'on layer sothat the anti-foggantis inat least one=of the-layers. In 'these cases,we'use the same or a slightly greater ratio of rare metal-- salt tosilver halide than whenthe salt is in cue-1111 11151011 layer. That is,the inhibitingcomeuna's". maylbe used in a colloid layer-suchasageiauri' subbin'gor overcoating layer contiguous" tofadJ'acent to, or ncontact with the emulsionla'yei'. When used -in this way; the compoundsstabili'z'e'thfe emulsiori'when it is aged over long periods of timeespecially under non-ideal con-- ditibris'of temperature and humidity.In such"- cases theamount of the compound per unit area should be the-same; per kilogram" of silv'er nitifat convertedt silver halide, aswould be used 3 ili'tll' saini'llfiit' area of the emulsion if'the compouriaweredn the emulsiofi'la'yerl v The fog' inhibitih'g ,age'rits'whichwe have' de-" scribed" may .bdu'sed iii va ious kinds of hotographic emulsions. Inadditiori" tdbeing useful in ordinary nonsens'itized emu'lsio'r'isthey may alsojbe' 'j used" in 'orthochromatic;anchromatic; and x r ay emulsions. If 'used WitHsensiti Zing' dySZ theymay be added the emulsionbefore "after th'fdyes' aread'ddfVarioussilver"salts of these. The dispersing agents may be gelatin orother colloid such as collodion, albumen, cellulose derivatives, orsynthetic resins.

It will be understood that we contemplate as included within ourinvention all modifications and equivalents falling within the scope ofthe appended claims.

What we claim is:

1. A silver halide emulsion containing an anionic palladium complex saltselected from the group consisting of alkali metal and alkaline earthmetal thiocyanato palladites, alkali metal and alkaline earth metalnitritopalladites, alkali metal and alkaline earth metalbromo-nitritopalladates and ammonium nitritopalladite.

2. A silver halide emulsion containing an alkali metal thiocyanatopalladite.

3. A silver halide emulsion containing an alkali metal nitritopalladite.

4. A silver halide emulsion containing ammonium nitritopalladite.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,120,429 Willis Dec. 8, 19141,120,580

Willis Dec. 8, 1914

